The present invention relates to a built-in antenna for a portable wireless unit, which exhibits high radiation characteristics even under various use conditions of the wireless unit.
In the specification, the term xe2x80x9cportable wireless unitxe2x80x9d involves a wireless information terminal, such as a music distribution dedicated terminal not having the speech function, in addition to a portable telephone set and PHS (trade mark).
By convention, the portable wireless unit, e.g., portable telephone set or PHS, uses a whip antenna of the telescopic type or a planar inverted-F antenna for its antenna.
The antenna described in the specification of U.S. Pat. No. 5,204,687 may be enumerated for the whip antenna of the telescopic type, used for the portable telephone set. The telescopic type whip antenna is constructed such that an electrically insulated helical antenna is mounted on the tip of the monopole antenna. When it is extended, it serves as a monopole antenna, and when it is contracted and put within the housing of the portable telephone set, it functions as a helical antenna.
The planar inverted-F antenna is disclosed in Japanese Unexamined Patent Laid-Open No. 103406/1981. In the example described in this publication, the planar inverted-F antenna is expanded to have a planar structure, and the peripheral length of the planar element is the half wavelength, and small. When the planar inverted-F antenna is disposed at an end of a ground plate of the housing of the portable telephone set, the planar inverted-F antenna has a relatively broad band characteristic. Further, the planar inverted-F antenna has a structure, which presents an impedance matching function. Therefore, it is advantageous in that there is no need of providing an impedance matching circuit outside the housing.
A normal portable telephone set, as shown in FIG. 12, includes both of a whip antenna attached to the outside of the portable telephone set and a planar inverted-F antenna mounted in the housing. The signals received by those antennae are switched from one to the other and vice versa in a diversity manner. Exactly, the signals received by those antennae are compared in level, and the antenna of which the signal level is the higher of those signal levels is selected, and a communication is performed.
In the portable telephone set shown in FIG. 12, a monopole antenna 27 and a planar inverted-F antenna 30 operate independently, and those antennae do not operate as a called composite antenna. A radio frequency switch 33 selects the monopole antenna 27 or the planar inverted-F antenna 30 depending on the received signal levels, as mentioned above.
An impedance matching circuit 34 matches a feeding point impedance of the monopole antenna 27 to 50 xcexa9. The planar inverted-F antenna 30 is a conductive plate of which the peripheral length is set to be about the half wavelength of the operating frequency. It is arranged in parallel with a ground plate 26, while being spaced by 4 mm, for example. A feeding point 32 is provided at a point which is on one side of the planar inverted-F antenna 30 and spaced from a earthing portion 31 by a fixed distance, e.g., 3 mm. A radio frequency signal derived from the impedance matching circuit 34 of the monopole antenna 27 or a radio frequency signal derived from the feeding point 32 of the planar inverted-F antenna 30 is selected by the radio frequency switch 33. In FIG. 12, a helical antenna 28 is connected through an insulating portion 29 to the tip of the monopole antenna 27.
Directivity patterns of the antennae of FIG. 12 are depicted in FIGS. 13 and 14 by using the coordinates illustrated aside in FIG. 12. FIG. 13 shows a directivity pattern of the monopole antenna 27 when it is selected, and FIG. 14 shows a directivity pattern of the planar inverted-F antenna 30 when it is selected. In FIG. 13, a solid line 35 indicates a vertically polarized wave component, and a broken line 36 indicates a horizontally polarized wave component. In FIG. 14, a solid line 37 indicates a vertically polarized wave component of the received radio wave, and a broken line 38 indicates a horizontally polarized wave component.
In the monopole antenna 27 shown in FIG. 13, an average level of the vertically polarized wave component 35 is higher than that of the horizontally polarized wave component 36. The vertically polarized wave component 35 has a pattern resembling that of the directivity of an 8-shaped half wavelength dipole. In the planar inverted-F antenna 30 shown in FIG. 14, the horizontally polarized wave component 38 is relatively high, and the vertically polarized wave component 37 has a butterfly-shaped pattern directivity since the antenna current is distributed in the ground plate 26.
A horizontal plane pattern average gain (referred to as PAG) is generally used for an evaluation index used for evaluating the antenna character of the portable telephone set. In a state that a human body equipped with a portable telephone antenna is positioned at the center of a spherical coordinate system, and the head of a human body is directed in the zenithal direction (Z direction), the PAG is given by                     PAG        =                              1                          2              ⁢              π                                ⁢                                    ∫              0                              2                ⁢                π                                      ⁢                                          [                                                      G                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      ⁡                                              (                                                                              π                            2                                                    ,                          φ                                                )                                                                              +                                                            1                      XPR                                        ⁢                    G                    ⁢                                          xe2x80x83                                        ⁢                                          φ                      ⁡                                              (                                                                              π                            2                                                    ,                          φ                                                )                                                                                            ⁢                                  xe2x80x83                                ]                            ⁢                              ⅆ                φ                                                                        [                  Formula          ⁢                      xe2x80x83                    ⁢          1                ]            
In the above equation, Gxcex8 (xcfx86) and Gxcfx86 (xcfx86) are power directivities of a vertically polarized wave and a horizontally polarized wave in the X-Y plane.
A general cross-polarization power ratio XPR of a mobile communication unit in a multiple wave environment is expressed by a ratio of the vertically polarized wave component to the horizontally polarized wave component, and is 4 to 9 dB, as known. This ratio is calculated on the assumption that the vertically polarized wave component of an arriving wave is higher than the horizontally polarized wave component by 4 to 9 dB. Accordingly, in the radiation pattern of the antenna, the vertically polarized wave component is weighted by XPR. Substantially in the specification, description of the XPR will be given by using 9 dB as a general value in an urban area. Thus, in the antenna of the portable telephone set, a high PAG is obtained by increasing the vertically polarized wave component when it is in use.
The PAG is generally xe2x88x927 dB when the portable telephone set is in a speech communication state and the whip antenna is extended, and this value is a target value of the performance of the main antenna contained.
Recently, it is demanded to completely build the main antenna into the portable telephone set, in place of the antenna being protruded outside, such as the whip antenna. In this case, the performance comparable with that of the external whip antenna is required for the built-in main antenna, as a matter of course.
In the conventional built-in type planar inverted-F antenna, however, in the speech communication state that the user grips the portable telephone set and moves it close to his ear, reduction of the radiation efficiency of the antenna is great since the distribution of the antenna current is present in the ground plate of the portable telephone set. For this reason, the PAG of the antenna is lower than that of the whip antenna being extended, approximately xe2x88x9211 dB. It is confirmed that when the portable telephone set is put close to a metal table, the antenna gain reduces, and the value of the PAG is lowered to about xe2x88x9216 dB.
When the portable telephone set is placed on the metal table, the conventional whip antenna is frequently stored in the housing. In this case, the helical antenna 28 shown in FIG. 12 operates. The helical antenna 28 is close to the metal table, and its axial direction is parallel to the metal disk, and its gain is reduced through its electromagnetic interaction with the metal, and the PAG is about xe2x88x9218 dB.
One of the main use conditions of the portable telephone set is that the user grips the portable telephone set, and moves it close to his ear, and talks with another party while slanting it at about 60xc2x0. In the PHS telephone set, the moving image distribution together with voice speech, and the video telephone service have started. (Reference is made to the magazine xe2x80x9cNikkei Communicationxe2x80x9d published by Nikkei Business Publications, Inc, issued Sep. 18, 2000, pp 113 to 115.)
Further, the music delivery service has started by using the wireless information terminal having no communication function. In using each of those devices, the user operates the device in a state that it is positioned near his ear as in the normal voice speech. In an additional case, he grips the device and holds it in front of his chest pocket, and in this state, he operates the device. In a further case, he puts the device in his chest pocket and in this state he operates the device.
In a case where the portable telephone set is put in the chest pocket, the orientation of the telephone set is not fixed. If the planar inverted-F antenna is mounted on one of the sides of the portable telephone set, there is the possibility that the antenna is directed to the human body. In this case, the reduction of the radiation efficiency is great, and the PAG is about xe2x88x9210 dB, and low.
Accordingly, an object of the present invention is to provide an antenna built in the a portable wireless unit which retains a high radiation efficiency in various use conditions, and is simplified at the manufacturing stage.
(1) To achieve the above object, there is provided a built-in antenna for a portable wireless unit including a conductive antenna element disposed along the inside of a housing at an upper end of a portable wireless unit, the conductive antenna having a monopole part defined as a part of a length of a substantially half-wavelength of the conductive antenna; an inverted-F antenna part defined as the remaining part of a length of a substantially xc2xc wavelength of the conductive antenna; and an antenna feeding point provided at a position near an earthing part of the inverted-F antenna part; wherein the inverted-F antenna part is disposed parallel to a ground plate surface within the housing of the portable wireless unit and parallel to the upper end of the portable wireless unit and one end of the inverted-F antenna part is connected to the ground plate as the earthing part.
With such an arrangement, the antenna may be built in the portable wireless unit with a simple construction which does not requiring the impedance matching circuit. The antenna gain when the portable wireless unit is in speech communication state or placed on a metal table, is improved.
(2) In the built-in antenna for a portable wireless unit, the inverted-F antenna part is disposed along the long side of the portable wireless unit.
With this feature, a high antenna gain is improved in the hand-holding operation state and speech communication state, and in a state that the portable wireless unit is placed on the metal table.
(3) There is another aspect of the invention, there is provided a built-in antenna for a portable wireless including a conductive antenna element disposed along the long side of the inside of a housing, the conductive antenna element having a monopole part defined as a part of a length of a substantially half-wavelength of the conductive antenna element; an inverted-F antenna part defined as the remaining part of a length of a substantially xc2xc wavelength of the conductive antenna element; and an antenna feeding point provided at a position near an earthing part; wherein one end of the inverted-F antenna part is connected, to the ground plate as an earthing part, and the inverted-F antenna part is disposed parallel to the ground plate of the housing of the portable wireless unit and along the long side of the inside of the housing.
With this feature, a high antenna gain is improved in the in-chest-pocket state, the hand-holding operation state and speech communication state, and in a state that the portable wireless unit is placed on the metal table.
(4) In the built-in antenna for a portable wireless unit, the inverted-F antenna part is disposed parallel to the ground plate of the housing of the portable wireless unit, and parallel to the upper end of the inside of the housing.
With this feature, a high antenna gain is improved in a state that the portable wireless unit is, at will, put in a chest pocket, the hand-holding operation state and speech communication state, and in a state that the portable wireless unit is placed on the metal table.
(5) The built-in antenna for a portable wireless unit further includes fixing means for fixing the antenna element to the rear side of the housing, and contacting means for making the earthing part and the feeding point of the antenna element contact with a printing pattern on a circuit board.
This feature simplifies the manufacturing process of manufacturing the built-in antenna, leading to the productivity improvement.